Method for performing replacement of a subscriber identity module (SIM) in a mobile communications network

ABSTRACT

In a mobile communications network, each subscriber is allocated a unique identity code and is provided with a card (a SIM card) bearing that code which provides subscriber access to the system. A list of identity codes together with corresponding subscriber details are stored in a first store. When a card is to be replaced, a new identity code is created for the subscriber and is stored in the first store and in a second store. A mapping is provided between the new identity code and the corresponding existing subscriber identity code. The new identity code is then associated with the corresponding subscriber details and is activated while the existing code is de-activated.

This invention relates to mobile telecommunications systems and to theidentification of subscribers in such a system. In particular, theinvention relates to the provision of subscriber identity cards wherebysubscribers are identified and authorised to use the system.

BACKGROUND OF THE INVENTION

A particular problem in mobile telephone systems to which the publichave access is that of fraudulent misuse, the most common form of fraudbeing the use of stolen or cloned handsets to evade the call billingprocess. This represents a significant loss of revenue to systemoperators. An approach to this problem has been the introduction ofhandsets which require the insertion of a subscriber identity cardcontaining coded information before access to the system is permitted.For example, the GSM system requires the use of a subscriber identitymodule (SIM) card to allow a mobile terminal to use the system services.

It will be appreciated that a subscriber identity card will have afinite lifetime and will from time to time require replacement on anoccasional basis as a result of loss by the subscriber or, morecommonly, on a periodic basis to allow for normal wear and tear. Thisprovides a problem to the system operator if security is to bemaintained. To prevent fraud, the system is arranged to recognise aunique card for each subscriber. However, this requirement is generallyincompatible with the temporary existence of two cards during thereplacement operation. One approach to this problem is described inspecification No. EP-A2-0481714 and No. GB-A-2248999 which describe theuse of a SIM card or smart card to control access to a mobile system. Inthis arrangement, the first use of a replacement card triggers deletionof the replaced card from the system records. This process however isreliant upon diligence by the subscriber in using the replacement cardpromptly so that the change can be put into effect.

The object of the invention is to minimise or to overcome thisdisadvantage.

A further object of the invention is to provide a greater degree ofcontrol by the system operator on the card replacement process.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of effectingsubscriber identity card replacement in a mobile communications networkin which each subscriber is allocated a unique identity code, the methodincluding storing a list of said identity codes together with subscriberdetails in a first store, creating a new identity code for a saidsubscriber and storing said new code in said first store and in a secondstore, providing a mapping between the new identity code and thecorresponding existing subscriber identity code, associating timinginformation with the new identity code, and associating the new identitycode with the corresponding subscriber details at, or after, a timedetermined by the timing information, whereby to activate the new codeand deactivate the existing code.

A further aspect of the invention provides an arrangement for effectingsubscriber identity card replacement in a mobile communications networkin which each subscriber is allocated a unique identity code, thearrangement including a first store for storing a list of said identitycodes together with corresponding subscriber details, a second store forstoring each said code together with a status indicator whose valuedetermines whether that identity code is activated or deactivated, meansfor generating a new identity code for a subscriber, for providing amapping between that new identity code and the corresponding existingsubscriber identity code and for associating timing information with thenew identity code, and means for associating the new identity code withthe corresponding subscriber details at, or after, a time determined bythe timing information whereby to activate the new code and deactivatethe existing code.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference tothe accompanying drawings in which:

FIG. 1 is a schematic diagram of a mobile communication system;

FIG. 2 is a flow chart illustrating the procedure for facilitating cardreplacement in the system of FIG. 1; and

FIG. 3 is a flow chart illustrating a scheduling procedure for effectingsubscriber IMSI record updating in the system of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIG. 1, there is depicted in highly schematic form part ofa mobile cellular communications network or system. The service area ofthe system is subdivided into a plurality of contiguous cells 11 in eachof which mobiles 10 are serviced via a respective base station 12.Operation of a group of base stations 12 is controlled via a basestation controller 13 and, in turn, a number of base station controllersare serviced by a mobile switching centre (MSC) 14 which may provide aninterface to the public telecommunications network. With thisarrangement, the mobile switching centre 14 may service, via the basestation controllers 13 and the base stations 12, typically over onehundred individual cells 11. Information relating to the mobiles 10within the service area of the mobile switching centre 14 is stored in avisitors location register or database 16 associated with the switchingcentre. The system also incorporates a master database 17 of subscriberinformation, this master database commonly being referred to as a homelocation register (HLR). When a mobile enters the service area of theMSC 14 it registers with that MSC. As part of the registrationprocedure, information relating to that mobile is retrieved from thehome location register and stored in the visitors location register.

In the system of FIG. 1, each mobile terminal 10 requires the insertionof a respective card or subscriber identity module 110 bearing unique,subscriber specific information that is used to authorise access to thesystem by the terminal. This information includes a subscriberidentification code which, in the GSM system, is referred to as theinternational mobile subscriber identity (IMSI). From time to time, thiscard will require replacement, the procedure for which will be describedbelow.

Referring now to FIG. 2, the home location register incorporates a firsttable GHLRAUTH containing a list of the currently authorised subscriberidentities or IMSIs. A second table GHLRDATA contains this list togetherwith a status indication for each entry. A third table GHLRSIMR providesfor correlation between an existing IMSI and a new IMSI with which it isto be replaced. When a subscriber card is to be replaced, the new IMSIfor this replacement card is added by the system operator to the tableGHLRAUTH in the same way that the IMSI of a new subscriber would beentered. This causes automatic addition of an entry in table GHLRDATAfor this IMSI together with a status indicator D indicating that theIMSI is currently deactivated. The new IMSI is next added to tableGHLRSIMR. This causes the status indicator for the IMSI in tableGHLRDATA to be changed to R indicating a replacement. The arrangement issuch that the new IMSI cannot be entered in table GHLRSIMR unless itsstatus indicator in table GHLRDATA has already been set to D, i.e.deactivated. Also, once a new IMSI has been added to the table GHLRSIMR,the operator is prevented from provisioning any basic or supplementaryservices against it while the current IMSI is still active. Of course,no such restriction applies to the current IMSI. However, both IMSIsmust be present in both the GHLRAUTH and GHLRDATA tables before entry ofthe new IMSI in the GHLRSIMR table.

When adding an entry to the table GHLRSIMR, the following information isprovided:

The new IMSI.

The current IMSI.

An option code used to indicate the manner in which the change is to beeffected.

The activation time, i.e. the time from which the new card may be used.

The invocation time, i.e. the time from which the new card must be usedand the current card becomes invalid.

There are three options available for performing the changeover ofcards. These are scheduled changeover, user triggered changeover andforced changeover. The way in which these options are performed will bediscussed below.

Scheduled changeover is the preferred method of operation and is thesimplest way of managing SIM card replacement. The operator datafillsthe new IMSI and the current IMSI in the GHLRSIMR store, sets the optionfield to FIXED and specifies an invocation time which determines theearliest time at which the changeover may take place. A scheduler isused to determine the precise time at which changeover is to occur andprocesses all GHLRSIMR entries with that time stamp or an earlier timestamp. The functioning of the scheduler is illustrated in the flow chartof FIG. 3. At regular intervals, e.g. every hour, the scheduler scansthe GHLRSIMR table looking for entries whose invocation time has beenreached. When such an entry is found, i.e. it is determined that the newSIM card (IMSI+Ki) is to become the active one the changeover procedureis initiated. The changeover is effected by making the new IMSI use therecords previously used by the old IMSI. After changeover, the memorypreviously associated with the new IMSI is deallocated and the old IMSIis removed from level indexing. The tasks performed at changeover are asfollows.

1. Copy the authentication data and IMSI from the new IMSI record intothat of the old IMSI.

2. Wipe out the unprotected data in the old IMSI record.

3. Copy the old IMSI and old location data into the record used by thenew IMSI and mark the record as deleted.

4. Exchange the Subscriber Access Index stored in level indexing for thetwo IMSIs; i.e. the new IMSI is now mapped to the Subscriber AccessIndexes associated with the old IMSI and vice versa.

If the audit is not completed within the allocated time period, e.g.within one hour, the procedure is terminated and the next hourly auditis invoked. Thus, during busy periods, some changeovers may be delayeduntil a later audit.

In a preferred embodiment, we reduce the time that would be wasted byperforming the hourly audit when there is no useful work to be done,i.e. there is no IMSI currently requiring updating. This is achieved bythe use of the following time stamps.

EARLY_ACT_STAMP: This time stamp records the earliest activation time(after the present) of a GHLRSIMR entry. When adding an entry toGHLRSIMR, if the activation time is earlier than the current value thenGHLRSIMR is updated with the new value.

EARLY_INV_STAMP: This time stamp records the earliest invocation time ofa GHLRSIMR entry. EARLY_INV_STAMP is updated in a similar way asEARLY_ACT_STAMP except that the invocation time is checked.

To make use of the two time stamps, the scheduler effects two checksbefore scanning the GHLRSIMR.

If EARLY_ACT_STAMP is later than the present time, the table is the OM(SMPREND)

If EARLY_INV_STAMP is later than the present time then the table is notscanned to find IMSls to changeover.

User triggered changeover is a flexible way of managing SIM replacementgiving the subscriber the choice, within limits, of when the changeoveris to take place. The subscriber triggers the changeover by replacingthe old SIM card with the new card in the handset thus initiating anupdate location. The operator datafills the new IMSI and the currentIMSI in the GHLRSIMR, sets the option field to USER and provides theactivation and invocation times. The activation time is the time fromwhich the subscriber is permitted to trigger the changeover. Theinvocation time is the time at which the changeover is scheduled to takeplace if the subscriber has not yet triggered the changeover byinsertion of the new card.

Forced changeover is used in the exceptional circumstances thatchangeover must be effected immediately. The operator sets up thesubscriber for scheduled or user triggered changeover as describedabove. Once the new IMSI has been added to GHLRSIMR, the operator maytrigger the changeover immediately.

It will be understood that although the above card replacement techniquehas been described with particular reference to the GSM mobile system,it is by no means limited to use with that particular system but is ofgeneral application to mobile systems.

What is claimed is:
 1. A method of effecting subscriber identity cardreplacement in a mobile communications network in which each subscriberis allocated a unique identity code that is associated with informationstored on the card, the method including storing a current identity codetogether with respective subscriber details as a first record in a firststore, storing said current subscriber identity code in a second storetogether with a status indicator indicating an active nature of thatidentity code, creating a replacement identity code for said subscriber,storing said replacement code in said first store together with thesubscriber details as a second record, storing said replacementsubscriber identity code in the second store together with a statusindicator indicating a de-activated nature of that identity code,storing in a third store data incorporating timing information andproviding a correlation between the replacement subscriber identity codeand the current subscriber identity code allocated to that subscriber,changing the status indicator of the replacement code to indicate areplacement nature of the replacement code in the second store, and, ata time determined from said timing information in said third store,exchanging said current and replacement subscriber identity codesbetween said first and second records so as to associate the replacementsubscriber identity code with the subscriber details in the firstrecord, activating the replacement subscriber identity code and deletingsaid second record so as to maintain the first record containing thereplacement subscriber identity code as the sole active record.
 2. Amethod as claimed in claim 1, wherein a new subscriber identity code canbe entered into the third store only if that identity code together withthe corresponding existing code which it is to replace are present inboth the first and second stores and the status indicator of that codein the second store is indicative of a deactivated condition of thatcode.
 3. A method as claimed in claim 2, wherein each new subscriberidentity code stored in the third store is provided with a correspondingoption code indicative of the manner in which that new code is toreplace the corresponding existing code.
 4. A method as claimed in claim3 wherein a network scheduler initiates the step of associating the newidentity code with the corresponding subscriber details.
 5. A method asclaimed in claim 4 wherein the timing information determines a timeafter which a subscriber can initiate the step of associating the newidentity code with the corresponding subscriber details.
 6. A method asclaimed in claim 5 wherein the timing information further determines atime after which, if the subscriber has not initiated the associatingstep, a network scheduler initiates the associating step.
 7. Anarrangement for effecting subscriber identity card replacement in amobile communications network in which each subscriber is allocated aunique identity code that is associated with information stored on thecard, the arrangement including a first store for storing a currentidentity code together with respective subscriber details as a firstrecord and for storing a replacement code in said first store togetherwith the subscriber details as a second record, a second store forstoring said current subscriber identity code together with a statusindicator indicating an active nature of that identity code and forstoring said replacement subscriber identity code together with a statusindicator indicating a de-activated nature of that identity code, athird store for storing data incorporating timing information andproviding a correlation between the replacement subscriber identity codeand the current subscriber identity code allocated to that subscriber,means for changing the status indicator of the replacement identity codeto indicate a replacement nature of the replacement code in the secondstore, means for exchanging, at a time determined from said timinginformation, said current and replacement subscriber identity codesbetween said first and second records so as to associate the replacementsubscriber identity code with the subscriber details in the firstrecord, and means for deleting said second record so as to maintain thefirst record containing the replacement subscriber identity code as thesole active record.